[E-Daily Reporter Lee Ji-hyun ] Contrary to concerns that COVID-19 vaccination increases the risk of cancer, a study analyzing 36.02 million people in South Korea found no clear increase in cancer incidence. The study tracked cancer incidence trends for 50 months following vaccination and found no statistically significant changes compared to the past.

Professor Jeong Jae-hoon of the Department of Preventive Medicine at Korea University College of Medicine made these remarks during a science media briefing on the 29th while explaining the findings of two studies recently published in international academic journals. On the 22nd, the research team published a paper titled “Impact of SARS-CoV-2 vaccination on cancer trends: a nationwide interrupted time series study” in the international journal *Biomarker Research*.

Using data from the National Health Insurance Service, the research team analyzed cancer incidence trends among 36,024,394 individuals born between 1955 and 2004. The analysis period spanned a total of 176 months, from February 2011 to September 2025. Within this period, the researchers compared cancer incidence trends over the 50 months following August 2021—when vaccination efforts began in earnest—with those of the preceding decade or so.

The analysis found no statistically significant evidence of a sudden increase in incidence rates or an accelerated rate of increase following vaccination across all 13 cancer categories. The same results were observed in separate analyses of stomach, colorectal, lung, and prostate cancers. Although 89.3% of the study participants had received at least one dose of the COVID-19 vaccine, cancer incidence rates generally remained consistent with past trends.

The research team also published a paper titled “No Additional Cancer Risk Associated With Adenoviral Vector COVID-19 Vaccine Compared to mRNA Vaccines: A Nationwide Matched Cohort Study,” published online on September 10, compared the risk of cancer incidence based on vaccine type.

A comparison of 1,191,453 recipients of the AstraZeneca vaccine with 1,191,453 recipients of mRNA vaccines, such as Pfizer and Moderna, revealed no statistically significant difference in risk across 12 cancer types during the approximately three-year follow-up period.

This study was conducted to re-examine the controversy that arose after a group of Korean researchers reported a statistical association between COVID-19 vaccination and the diagnosis of certain cancers last September. That earlier study analyzed health insurance data from approximately 8.4 million people in the Seoul area and found that certain cancer diagnoses were observed more frequently among vaccinated individuals. However, it did not prove a causal relationship between the vaccine and cancer.

Professor Jeong pointed out that the limitations of the previous study included a short observation period and differences in characteristics between vaccinated and unvaccinated individuals. Generally, it takes several years or more for cancer to develop, yet the previous study showed differences in cancer diagnoses beginning shortly after vaccination. It is also possible that cancer was detected more frequently because vaccinated individuals undergo health screenings and seek medical care more frequently.

Professor Jeong explained, “If an association of the magnitude suggested by previous studies actually existed, an increase in cancer incidence should have been observed in South Korea, where the vast majority of the population has been vaccinated.” He added, “However, no such change was confirmed in nationwide trends.”

However, the research team emphasized that these results do not fully establish a long-term causal relationship between the vaccine and cancer incidence. They noted that it is difficult to completely rule out the effects of reduced cancer screenings during the COVID-19 pandemic and the subsequent recovery in healthcare utilization, and that additional follow-up is needed to assess the long-term risk of cancer.

Medical professionals expect this study to serve as evidence to alleviate vaccine-related anxiety. Eom Joong-sik, a professor of infectious diseases at Gachon University Gil Medical Center, said, “Since the previous paper went viral, there have been cases where the elderly and immunocompromised patients refused vaccination out of concern for cancer incidence,” adding, “This study can be useful in alleviating the anxiety of patients who absolutely need to be vaccinated.” He further emphasized, “COVID-19 continues to circulate annually, and high-risk groups are still experiencing hospitalizations and severe cases,” adding, “It is crucial to reduce vaccine hesitancy based on scientific evidence and ensure that high-risk groups continue to receive vaccinations.”